This invention relates to copy protection of a video signal and, more particularly, to a technique for superposing on that portion of the video signal which does not contain useful picture information copy protection information which includes information representing the number of successive generations of copies that can be made from the video signal.
Various techniques and formats have been proposed to prevent video signals from being copied, or dubbed, without authorization. For example, it is preferable in many environments to permit a video signal to be displayed as a video picture on, for example, a television monitor, but to prevent that same video signal from being recorded by a video recorder. The video signal may be transmitted via cable, direct satellite broadcast (DSB) or over-the-air; or the video signal may be recorded on a video tape or a video disk. In the field of sales or rentals of video tapes and video disks, substantial amounts of revenues will be lost if a user is permitted to make a copy of the video program on a video tape or disk, thereby depriving the originator or distributor of the video tape or video disk of additional sales or rentals. Even though the unlawful re-recording or dubbing of such video programs may constitute copyright infringement, the threat of prosecution therefor presents little if any deterrent to such unlawful copying. Consequently, more positive approaches have been adopted to prevent a user from making an unauthorized copy of a video program in the form of a video recording thereof.
In one anti-copying scheme the video signal is modified to defeat the satisfactory operation of a typical video recorder yet still permit the display of an acceptable video picture therefrom. This is achieved by reducing the number of vertical synchronizing pulses included in the vertical blanking interval, thereby defeating the servo locking operation of the typical video recorder but permitting adequate detection of the vertical synchronizing pulses in the usual television receiver sync detector. In another proposal high amplitude pulses are inserted into a normally blank line interval of the vertical blanking interval so as to cause the usual automatic gain control (AGC) circuitry in a typical video recorder to reduce the recording level of the signal recorded thereby, resulting in a recorded video signal whose amplitude is effectively zero.
As yet another example, it has been proposed to superpose a copy inhibit pulse on, for example, the equalizing or vertical synchronizing pulses normally included in the vertical blanking interval and to include in the recording channel of a video recorder a detector which operates to inhibit the recorder from operating in a record mode upon detecting this inhibit pulse.
While there is merit to each of the foregoing proposals, none of them addresses the problem of permitting one copy of the video signal from being made but prohibiting the copy from being copied further. In many situations it may be desirable to permit a consumer to make one copy directly from a video signal (whether that video signal is broadcasted or reproduced from a video tape or video disk) but the number of successive generations of copies is to be controlled. For example, a first generation may be permitted but a second generation may be prohibited. As another example, first and second generations may be permitted but a third generation may not (i.e. a recording and a re-recording may be permitted but a re-re-recording may be prohibited). In the foregoing copy protection schemes, if a video signal is permitted to be copied, a copy of the copied signal may be made and successive generations likewise may be made. But if a video signal is prohibited from being copied, even a single generation copy cannot be made. That is, prior proposals have not considered what is referred to herein as a serial copy management system (SCMS).